It is conventional practice in the art of electrohydraulic servo control systems to provide a command signal indicative of position, velocity, acceleration or pressure desired at the controlled mechanism, to measure actual position, velocity and acceleration at the controlled mechanism by means of corresponding transducers, and to drive a hydraulic actuator with an error signal representative of a difference between the command signal and the measured motion variables. Provision of three transducers mounted on or otherwise responsive to the controlled mechanism increases significantly the overall expense of the servo system while at the same time reducing overall reliability. The aforementioned deficiencies are particularly acute in the field of industrial robotics where interest in cost, simplicity and reliability is continually increasing.
U.S. patent application Ser. No. 418,086, filed Sept. 14, 1982 and assigned to the assignee hereof, now U.S. Pat. No. 4,502,109, discloses an electrohydraulic servo control system having three dynamic state variables, namely position, velocity and acceleration. A control system includes a sensor coupled to the hydraulic actuator for measuring load position, and a digital observer responsive to measured position for estimating velocity and acceleration. Signals indicative of measured and/or estimated state variables are compared with an input state command signal to obtain a difference of error signal which drives the actuator. The observer electronics includes a digital microprocessor suitably programmed to estimate the state variables as solutions to corresponding linear equations. The several equation constants, which are functions of actuator and driven mass characteristics, are entered through a corresponding multiplicity of operator-adjustable resistors. U.S. patent application Ser. No. 699,039, filed Feb. 7, 1985, now U.S. Pat. No. 4,581,699, as a continuation-in-part of Ser. No. 418,086, and likewise assigned to the assignee hereof, discloses a modification to the parent disclosure wherein the several equation constants are down-loaded from a remote system into observer storage registers.
Although the technology disclosed in the above-referenced patent applications presents a significant step forward in the art, improvement remains desirable in a number of areas. For example, the need to calculate the several state variables as solutions to a corresponding number of equations at each input sampling interval is quite time consuming, placing limitations on speed of operation and the number of tasks that can be performed. Furthermore, the requirement that system constants be loaded into the observer system limits adaptability of the system for changing conditions, such as wear or hydraulic fluid pressure variation.